Thermostat



Patented July 4, 1933 UNITED STATES PATENT OFFICE FRANK KUHN AND LAURENCE H. THOMAS, OF DETROIT, MICHIGAN, ASSIGNORS TO AMERICAN ELECTRICAL HEATER COMPANY, OF DETROIT, MICHIGAN, A GORPORA- TION OF MICHIGAN THERMOSTAT Application filed March 26, 1928. Serial No. 264,900.

The invention relates to thermostats and more particularly to a thermostatic switch device adapted to make or break an electric circuit at a certain predetermined temperature. Our invention is designed especially for use in automatic electric irons, although it is adapted also for other purposes.

One of the objects of the invention is to so construct the thermostatic elements as to eliminate spring members other than the thermostatic elements themselves while at the same time maintaining substantial pres sure between the contacts.

Another object is to design a simple thermostat construction adapted to automatically control the temperature of an electric iron when operatedon alternating current.

A further object is to provide a thermostat where the spring pressure between contact points may be maintained unimpaired at temperatures where ordinary springs are likely to lose their spring action.

These and other objects are attained by providing the construction hereinafter more fully described and illustratedin the accompanying drawing, wherein Figure 1 is a side View of the thermostatic switch device;

Figure 2 is a longitudinal section therethrough;

Figure 3 is a cross section on the line 33 of Figure 2; and

Figure 4 is a cross section on the line 44 of Figure 2.

Referring now to the embodiment of the invention as illustrated in the drawing, 10 and 11 represent bimetallic thermostatic strips laterally spaced from each other at one end by the spacer 12 and secured to a base or casing 13 by suitable means such as the riveted rod 1 1. Each bi-metallic strip extends outwardly from'its point of" support and the free ends thereof are provided with suitable contacts 15 and 16 respectively adapted to cooperate for completing an electric circuit. The two strips are otherwise insulated from each other, for example, by the mica sheet 17 interposed between the element 10 and the spacer 12. The thermostatic elements 10 and 11 are so constructed and arranged that under increasing temperature conditions both elements are deflected laterally in the same direction and in the construction shown both the elements 10 and 11 move away from the flange 18 of the base upon increase in temperature.

The thermostatic elements 10 and 11 when assembled are .arranged to have a certain tension between the contacts 15 and 16 due to the resiliency of the bi-metallic strips themselves. F or example, the strip 11 may be curved slightly toward the strip 10 to produce the desired. pressure between the contacts. The thermostatic element 10 is also preferably designed to have a greater lateral deflection per unit increase in temperature than the element 11 so that as the temperature rises the pressure between the contacts is somewhat increased due to the tendency of the following element 10 to deflect faster than the leading element 11. One method for accomplishing this result is to construct the element 10 of a slightly thinner bi-metallic strip than the element 11, thus causing the thinner strip to deflect at a greater rate than the thicker strip. It is also preferable to have the outer end of the element 10 provided with means for increasing the rigidity thereof, and as shown, this is accomplished by the laterally extending flanges 10a formed by bending the edges of the bl-metallic strip for a predetermined distance on opposite sides of the contact 15.

For breaking the circuit a stop is provided in the path of the thermostatic element 10, spaced in such a manner as to engage the outer'end thereof when the d 'fiGCtlOIl of the element corresponds to a predetermined temperature. able and as shown comprises a set screw threadedly engaging an upwardly extending flange 20 of the base 13. The thermostatic elements are adapted to be connected into a suitable electric circuit by terminals 21 and 22 respectively extending laterally of the respective elements. As shown, the terminal 21 is formed on the spacer 12 hearing against the element 10, while the terminal 22 is integral with a second spacer 23 contacting with This stop 19 is preferably adjust-- the element 11. 24 is a flange on the base 13 insulated from the spacer 23 by a mica sheet 25. For further insulating the elements from the base a mica sheet 26 is disposed between the element 10 and the flange 18.

In the construction as described, the circuit is normally closed when the thermostatic elements are at room temperatures by reason of the contacts 15 and 16 being in engagement. A certain pressure is maintained between said contacts as previously stated by reason of the resiliency of the elements themselves. Upon rise in temperature both thermostatic elements move laterally away from the flange 18 but the following element 10 tends to move at a faster rate than the leading element 11, thus maintaining at all times the pressure between the contacts. When the element 10 strikes the stop 19 the movement of said element is retarded and further increase in tem perature causes the element 11 to mom away therefrom and separate-the contacts 15 and 16. By adjusting the set screw 19 the ther mostat may be set to break the circuit at any predetermined temperature.

The construction above described is particularly adapted for use in controlling circuits at temperatures where ordinary spring metals do not maintain their resiliency and is designed primarily to be used on automatic electric irons where the working temperature of the iron is desired to be held in the vicinity of 500 F.

What we claim as our invention is:

l. A thermostatic switch comprising a pair of laterally spaced bi-metallic strips, each fixed at one end and having opposite ends in contact, said strips both being laterally movable in the same-direction under increasing temperature conditions, the following strip under such conditions being thinner than the leading strip and means for arresting movement of said "i nner strip.

2. A thermostatic switch comprising a bimetallic strip iized at one end and having the free end theret? movable laterally in a certain direction under increasing temperatures, a second bimetallic strip also having one end fixed and having the free end thereof movable in the aforesaid direction and provided with a contact point engageable with a corresponding contact point on the first-mentioned strip, said second strip having a smaller sectional area than said first strip and constructed to move at a faster rate than the first strip whereby pressure between the contact points is increased upon a rise in temperature, and means for arresting movement of the second strip at a predetermined point in its travel to permit separation of the strips.

3. A thermostatic switch comprising a bimetallic strip fixed at one end and having the free end thereof movable laterally in a certain direction under increasing temperatures, a second bimetallic strip also fixed at one end and having the free end thereof movable laterally in the aforesaid direction, said second strip having a substantially smaller cross sectional area than the first-mentioned strip whereby movement of the latter upon a rise in temperature is resisted by the second strip.

4. A thermostatic switch comprising a pair of cooperating contacts, a pair of thermostatic strips operatively connected to the respective cont-acts aforesaid and mounted to maintain a continuous contact pressure between said contacts under both rapid and slow temperature changes and means for arresting the following strip under rising temperature conditions to separate the contacts at a predetermined temperature.

5. A thermostatic switch comprising a pair of cooperating contacts, a pair of thermostatic strips operatively connected to the respective contacts aforesaid, said strips being laterally'movable in the same direction under increasing temperature conditions, the following strip under such conditions having a greater lateral deflection per unit increase in temperature than the leading strip thereby causing increased pressure between said contacts upon rise in temperature, and means for arresting movement of said following strip to separate said contacts at a predetermined temperature.

In testimony whereof we ailix our signatures.

FRANK KUHN. LAURENCE H. THOMAS. 

